1. Field of the Invention
The present invention relates to a system and method for detecting objects under the surface of the ground, and in particular, to three-dimensional imaging to detect an underground target item such as a mine.
2. Background of the Invention
Buried mines on, e.g., a beachhead, are a major threat to amphibious landing forces and a severe obstacle to a rapid amphibious landing. Clearing mines prior to a full-scale landing is a slow and tedious process that requires manual location and neutralization of the individual mines. This process includes the use of heavy machinery to detonate anti-personnel mines while, at the same time, facing the threat of larger anti-tank mines.
Ground penetration radar systems using transistor generated short pulses have been in use for decades for geophysical applications. These systems can be relatively compact, approximately the size of a lawn mower, and are generally pulled along the ground with the radar signal directed downwardly into the ground.
Recently, airborne (e.g., from an aircraft) synthetic aperture radar (SAR) has also been used in mine detection. SARs typically are side-looking radar which produce a two-dimensional image of the earth's surface. In the past, SARs operated with bandwidth up to 500 mHz or 1 GHz resulting in range resolution of 6 inches.
In addition to aircraft-based radar systems, ground-based two-dimensional SAR imaging systems have been used to locate buried mines. These ground-based SAR systems use an impulse radar disposed on an elevated platform and operated in a side-looking mode.
One disadvantage with current radar-based mine detecting systems is that these systems tend to be limited to generating only a two-dimensional image rather than a three-dimensional image. A two-dimensional imaging system has limited capabilities with respect to the accuracy and precision by which the mine detection system operates when compared with that potentially available with three-dimensional imaging system.
An additional disadvantage with current SAR systems is that these systems produce an image of limited resolution. Since SARs have operated at bandwidths up to 1 GHz, SAR range resolution is limited to about six inches, as indicated above. Consequently, the six-inch imaging resolution reduces the applicability of SARs in buried mine imaging, detection and classification because mines tend to be 3 inches to a foot in diameter.